1. Field of the Invention
The present invention relates to alloy-semiconductor radiation detectors with rectifying junction contacts, the formation of rectifying junction contacts on alloy-semiconductors using photo-electrochemical etching, the use of such alloy-semiconductor devices with rectifying junction contacts in PIN ionization detector devices, and systems and methods for revealing surface morphology of such alloy-semiconductors.
2. Description of the Related Art
Several methods have been developed for the external formation of P- and N-type contacts on CdTe and CdZnTe for Positive-Intermediate-Negative (PIN) devices. For example, X. Li, et al., xe2x80x9cEffect of nitric-phosphoric acid etches on material properties and back-contact formation of CdTe-based solar cells,xe2x80x9d Journal of Vacuum Science Technology A, 17(3), May/June, 1999; R. Sudharsanan et al., xe2x80x9cFabrication and characterization of CdZnTe radiation detectors with a new P-I-N design,xe2x80x9d presented at the 1996 U.S. Workshop on the Physics and Chemistry of II-VI Materials, 1996; A. Khusainov et al., xe2x80x9cPerformance of a high resolution CdTe and CdZnTe P-I-N detectors,xe2x80x9d Nuclear Instruments and Methods in Physics Research A, 380, 245-251, 1996; T. Narita et al., xe2x80x9cDevelopment of prototype pixellated PIN CdZnTe detectors,xe2x80x9d Proceeding of the SPIE, 3446, 1998; S. U. Egarievwe et al., Proceeding of SPIE, 3768, 1999; T Narita et al., xe2x80x9cDevelopment of IMARAD CZT detectors with PIN contacts,xe2x80x9d Proceeding of SPIE, 3768, 1999; M. Niraula et al., xe2x80x9cFabrication of CdTe detectors in a P-I-N design for gamma-ray spectroscopy,xe2x80x9d Proceeding of SPIE, 3768, 1999; M. Niraula et al., xe2x80x9cFabrication and performance of P-I-N CdTe radiation detectors,xe2x80x9d Nuclear Instruments and Methods in Physics Research A, 436, 132-137, 1999; and T. Takahashi et al., xe2x80x9cHigh-resolution Schottky CdTe diode for hard X-ray and gamma-ray astronomy,xe2x80x9d Nuclear Instruments and Methods in Physics Research A, 436, 111-119, 1999, all describe various methods for forming an external P-type and/or N-type contacts on CdTe and CdZnTe for PIN semiconductor devices.
However, all these methods suffer from several shortcomings. First, these conventional methods all involve sophisticated vacuum deposition equipment. This necessarily entails that production of semiconductor devices using such methods are expensive and difficult. Second, these conventional methods also require high temperature heating during formation of the contacts, which heating can cause degradation of semiconductor""s material properties. Third, because the metal used in the metal deposition process may be impure, the semiconductor device can become contaminated during the metal deposition process. Fourth, it is possible that the interface between the deposited metal and semiconductor device may have an oxide layer that can degrade device performance. Thus, there remains a need for an improved system and method for forming rectifying junction contacts in PIN alloy-semiconductor devices. There also remains a need for a PIN ionization detector device utilizing such alloy-semiconductor devices with rectifying junction contacts. Further, there remains a need for an efficient and inexpensive method for revealing surface morphology of alloy-semiconductors. These advantages have been obtained with the present invention.
Accordingly, it is an object of the present invention to provide a more efficient system and method for forming rectifying junction contacts in PIN alloy-semiconductor devices using photo-electrochemical, etching.
It is another object of the present invention to provide a more efficient system and method for forming rectifying junction contacts in PIN alloy-semiconductor devices in which there is no external contamination arising from impurities in the metal being deposited.
It is a further object of the present invention to provide a more efficient system and method for forming rectifying junction contacts in PIN alloy-semiconductor devices in which there is no oxide layer to degrade device performance.
It is still another object of the present invention to provide a more efficient system and method for forming rectifying junction contacts in PIN alloy-semiconductor devices, which method employs a room temperature process.
It is another object of the present invention to provide a more efficient system and method for forming rectifying junction contacts in PIN alloy-semiconductor devices in which fine contacts are produced easily.
It is a further object of the present invention to provide a more efficient system and method for forming rectifying junction contacts in PIN alloy-semiconductor devices in which there is lower leakage between adjacent contacts because the etch is recessed.
It is still another object of the present invention to provide a more efficient system and method for forming rectifying junction contacts in PIN alloy-semiconductor devices in which higher internal electric fields are possible, thereby improving charge collection.
It is another object of the present invention to provide a more efficient system and method for forming rectifying junction contacts in PIN alloy-semiconductor devices in which there is lower leakage current, producing an improved detector.
It is a further object of the present invention to provide a more efficient system and method for forming rectifying junction contacts in PIN alloy-semiconductor devices which results in lower production costs.
It is still another object of the present invention to provide a method for revealing surface morphology of alloy-semiconductors.
It is a further object of the present invention to provide a method for revealing surface morphology of such alloy-semiconductors such that high yields of single crystalline material can be obtained.
It is still another object of the present invention to provide a method for revealing surface morphology of such alloy-semiconductor which provides for visual mapping of the areas of maximum electron transport, which is closely related to good charge collection within a detector.
These objects, among others, have been obtained by means of a more efficient system and method for forming rectifying junction contacts in PIN alloy-semiconductor devices using photo-electrochemical etching. The present invention provides a means of creating rectifying junction contacts on alloy-semiconductor devices such as CdTe and CdZnTe, among others. In addition, the present invention also provides a simple and low cost method for revealing wafer surface morphology of alloy-semiconductors, thus providing an efficient and effective means for selecting single grain semiconductor substrates. Further, the present invention provides nuclear detectors employing such alloy-semiconductor devices having improved rectifying junctions as the detector element.